This invention relates to an organic electroluminescence device, and more particularly to an organic electroluminescence device which is constructed into a laminate structure including anodes, hole transport layers made of an organic compound, luminous layers made of an organic compound and cathodes laminated on each other and includes a plurality of fixed display segments and a method for manufacturing the same.
An organic electroluminescence device (hereinafter also referred to as "organic EL") is expected to be a device which is capable of being accommodated to a variety of applications extending from a back light and a fixed pattern display device to a dot matrix device.
A typical organic EL which has been conventionally known in the art is reported by Tang et al of Kodak in Appl. Phys. Lett. in 1987 and generally constructed as shown in FIG. 4. More particularly, the organic EL reported generally includes cathodes 31 each of which is an electrode made of Mg:Ag, Al:Li or the like, anodes 32 each of which is a transparent electrode made of indium tin oxide (ITO), light-emitting or luminous layers 33 and organic hole transport layers 34 laminated on each other and interposed between the cathodes 31 and the anodes 32, and a glass substrate 35 arranged on an outside of the anodes 32. The luminous layers 33 each are made of a thin film of an organic phosphor.
In the organic EL thus constructed, the luminous layer 33 made of the organic phosphor thin film has electrons and positive holes injected thereinto from the cathode 31 and anode 32. Then, the electrons and positive holes thus injected are subject to recombination to form excitons, so that display may be carried out utilizing emission of light (fluorescence or phosphorescence) obtained due to deactivation of the excitons. The light thus emitted is externally observed through the glass substrate 35.
Unfortunately, the conventional organic EL causes problems when it is used for fixed pattern display of increased density. More particularly, when a wiring of the cathode 31 is made of ITO inherently increased in specific resistance in the case that it is required to form a fine pattern by dynamic driving or to stretch wirings, a resistance of the wirings is caused to be increased, resulting in both non-uniform display and an increase in drive voltage being due to voltage drop through the wiring, leading to a failure to provide a fixed pattern display device of the dynamic drive type with high definition which has a wiring width as small as 0.1 mm or less. In order to address to the problem, it is required to remove a display section to carry out specific patterning such as, for example, a two-layer wiring or the like, to thereby correct the resistance, as disclosed in Japanese Patent Application Laid-Open Publication No. 307997/1993. Unfortunately, this causes a deterioration in productivity of the organic EL.
Another problem of the conventional original EL is that when a signal electrode is formed by forming a metal material for the cathode with a fine pattern while using ITO as a common electrode, it is required to subject the cathode 31 made of a metal film formed on the organic luminous layer 33 to patterning by dry processing. This is for the reason that water absorbed on the organic EL deteriorates quality of the organic EL to adversely affect performance thereof, therefore, it is substantially impossible to subject the organic EL to a wet treatment after formation of the organic layer. Thus, photolithography cannot be applied to formation of the cathode 31 which is a metal electrode. Substitutionally, mask deposition or patterning by laser is attempted for this purpose as disclosed in Japanese Patent Application Laid-Open Publication No. 3076/1993. However, the mask deposition substantially fails to render the patterning fine, to thereby reduce a degree of freedom in design of the original EL. Also, the patterning by laser requires to scan laser, resulting in being time-consuming and deteriorating productivity of the original EL.
Further, in the conventional original EL, the cathode 31 is made of a metal material decreased in work function such as Al:Li, Mg:Ag, Mg:In or the like. Thus, the organic EL has a further disadvantage that it is required to form a protective film of fluororesin such as SiO, GeO or the like on the cathode 31, because the cathode 31 is exposed on the organic luminous layer 33.